Robust wireless multimedia transmission in multiple in multiple-out (mimo) system assisted by channel state information

ABSTRACT

A system and method is provided wherein channel state information assisted MIMO transmission based on singular value decomposition (SVD) ( 204 ) ( 304 ) simplifies the decoding process. The present invention is a joint source and channel coding system and method for robust wireless multimedia communication. Using the fact that SVD redistributes the channel energy in a descending way, the base layer of the Fine-Grained-Scalability (FGS) ( 208 ) is mapped to the highest signal-to-noise (SNR) path to obtain better protection, while other enhancement layers are mapped to other paths such that less important layers are mapped to lower SNR paths in the SVD -decomposed channel. A multiple description code (MDC) ( 207 ) is also used in this manner such that at least one coded stream is provided more protection because of the high SNR. This invention pertains to any MIMO based wireless multimedia communication system.

The present invention relates to a MIMO based wireless multimediaCommunication system.

Multimedia transmission over wireless networks is becoming moreprevalent because of an increasing market demand. The constituent partsof current wireless communication protocols have been developed in anindependent fashion, without paying any particular attention to specifictransmission type needs. The physical layer, the MAC layer and thesource coding all have been developed independently. Each layer has beenoptimized to the greatest extent possible. The possibility to optimizethe system with joint source and channel coding has been identifiedwhich has the potential to increase the efficiency of a system withoutadding too much complexity in the system design. Much research has beendirected to finding better ways for the joint channel and source coding.J. P. Meehan and M. van der Schaar in “A Concept for Combined MPEG-4 FGSand Hierarchical Modulation for Wireless Video Transmission,” PhilipsResearch USA-TN-2001-044, 2001, the contents of which are herebyincluded by reference in their entirety, describe one such approach fora single antenna system by combining fine grained scalability (FGS)video coding with adaptive modulation.

Currently, available solutions for multimedia over a MIMO system areimplemented as follows. When an FGS or a multiple description code (MDC)coded system is transmitted over a MIMO system, all the streams receivethe same transmission power. Thus for FGS, the essential base layerneeds to be transmitted with a lower constellation while otherenhancement layers can be transmitted with a higher constellationmodulation. They are then transmitted using a different antenna. An MDCdoes not require different modulation for different source codedstreams. When using a MIMO for transmission, different streams can betransmitted on a different antenna. However, at least one stream must bereceived correctly so that the contents can be decoded. This approachonly takes advantage of spatial diversity over the MIMO system. It mayhappen that the channel condition is so bad that SNR on any of theTransmitter and Receiver antenna pairs is too low to deliver a reliabletransmission. For FGS, if the base layer is not correctly received, themultimedia contents cannot be recovered. For an MDC, if none of thestreams is received without error, the decoding cannot be accomplished.

The system and method of the present invention provides a joint channeland source coding scheme using Channel State Information (CSI) over aMultiple In and Multiple Out (MIMO) wireless communication system. Thesource coding can be FGS or multiple description code (MDC).

In a preferred embodiment, based on the CSI, the distribution of thetransmission energy in the channel is different for different streams.Consider a MIMO system. By some manipulation means, the signaltransmitted on an antenna pair 1 is allocated 80% of the entire energy,while signals on other antenna pairs are allocated the rest or 20% ofthe entire energy. This approach discriminates among antenna pairs andis accomplished in accordance with existing channel conditions at thetime of transmission. This means that antenna pair 1 is allocated thehighest SNR in the system. The higher SNR assigned to a pair makes itstransmissions more reliable than in a system in which energy is equallydistributed among antenna pairs. In this way, for FGS source coding thebase layer can be transmitted over the antenna pair that has the largestenergy assigned according to existing channel conditions. The result isthat the base layer enjoys the highest possible SNR over the MIMOchannel, while other enhancement layers can be transmitted with lowerSNR because they are not as important as the base layer.

For MDC source coding, one stream is transmitted over a high SNR channelwhile others are transmitted in some lower SNR channel. As long as onestream is reliably received, the multimedia stream can be decoded. Theaddition of an enhancement layer for FGS or more streams for MDC onlyincreases the quality of the video.

FIG. 1 illustrates CSI-assisted MIMO transmission by a wireless deviceaccording to the present invention;

FIG. 2 illustrates a flow diagram of the present invention; and

FIG. 3 illustrates a simplified block diagram of a wireless device in anad hoc wireless network according to an embodiment of the presentinvention.

In the following description, by way of explanation and not limitation,specific details are set forth such as the particular architecture,interfaces, techniques, etc., in order to provide a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practiced inother embodiments that depart from these specific details.

The system and method of the present invention provides a more robustmultimedia transmission within wireless networks by taking advantage ofthe channel state information (CSI). The CSI-assisted transmission ofthe present invention is combined with a source coding scheme thatoptimizes the wireless multimedia transmission system. Thus, the systemand method of the present invention is well suited to scalablevideo/audio transmission because it affords different protectionpriority to different video streams.

In the following sections, the first CSI-aided transmission in a MIMOsystem is described. Then, how the system and method of the presentinvention maps different multimedia streams onto different antennae ofthe system is disclosed.

In a preferred embodiment, a CSI-aided transmission in a MIMO system canbe achieved as follows. Using some measurements and feedback from thereceiver 102, a MIMO channel H can be made available at transmitter side101. Many feedback methods are possible. The preferred feedback methodis the simplest. The channel is estimated at the receiver side and thechannel coefficient is transmitted back to the transmitter as a normaldigital signal. While there are some issues with the feedback scheme,such as RF calibration to make the channel match, these issues can behandled in well-known ways to one ordinarily skilled in the art. Theonly assumption made herein is that the channel is quasi-static andreciprocal.

In this preferred embodiment, it is convenient to decompose theestimated channel matrix H_(n) by means of the Singular ValueDecomposition (SVD) so that

H_(n)=U_(n)D_(n)V_(n)′  (1)

where

(a) U_(n) and V_(n) are unitary complex matrices (i.e. U_(n) U_(n)′=I,etc.) of dimensions R×M and M×L respectively,

(b) D_(n) is a real diagonal matrix of dimension M×M containing, indescending order, the non-negative singular values of H_(n) (which arein fact the square roots of the eigen-values of H_(n) H_(n)′ or H_(n)′H_(n)), and

(c) the subscripts n are again a reminder of the noisy nature of thechannel estimate H_(n).

-   The received signal can then be expressed as

Y=HX+N=U _(n) D _(n) V _(n) ′X+N  (2)

where N is the white Gaussian noise with zero mean and variance σ².

The channel is SVD decomposed, while the signal is only multiplied bythe decomposed matrix from channel. The mapping is actually on a“logical” channel instead of the physical channel because after pre/postequalization (matrix from SVD), the signal is mapped to a logicalchannel with different Dn value.

In this preferred embodiment, the receiver estimates the channel and thereceiver performs the SVD decomposition. Then the receiver stores theU_(n) and D_(n) matrices and feeds back the V_(n) matrix to thetransmitter to multiply with data in the next packet, assuming thechannel will not change during this period. In an alternativeembodiment, the transmitter performs the SVD and feeds back the U_(n)matrix to the receiver after the SVD.

Since U_(n) 105 and V_(n) 106 are known at the transmitter side, priorto transmission the signal can be multiplied (pre-equalization) withV_(n) 106, and at the receiver side 102 the received signal can bemultiplied with U_(n)′ 104. Then equation (2) becomes

U _(n) ′Y=U _(n) ′H V _(n) X+N=U _(n) ′U _(n) D _(n) V _(n) ′V _(n) X+U_(n) ′V _(n) N=D _(n) X+N  (3)

in which different streams can be easily separated because D_(n) is adiagonal matrix. Since in D_(n) all the singular values are arranged indescending order, the first stream (signal) in X is allocated thelargest gain in the channel. Thus, this steam has the highest SNR forthe channel given.

Then, in all embodiments, different source coding streams are mappedonto the antennae. From the above description, it can be seen that thepath with the largest singular √{square root over (λ₁)} 108 holds thelargest SNR in the channel and, therefore, the base layer of FGS codecan be mapped onto it. The enhancement layers can be mapped to otherpaths with more important layers mapped onto the larger singular valuepaths. In this way, the more important layers are protected better withhigher SNR in the channel. For MDC streams, it really does not matterwhich stream maps to which singular value path because MDCs are equallyimportant and receiving any one of the MDC streams can result in correctdecoding of the multimedia source. However, at least one MDC stream mustbe correctly received. Given the uneven SNR distribution in the systemand method of the present invention, one MDC stream can always be sentin better channel condition, which increases its chances of being sentcorrectly.

Referring now to FIG. 2, a flow 200 of the procedure of the presentinvention is illustrated. At step 201 the Channel State Information(CSI) is determined. At the receiver, matrix H_(n) is estimated at step202 for MIMO channel H. At step 203 the estimated MIMO channel H_(n) isfed back to the transmitter from the receiver and then decomposed atstep 204 using Singular Value Decomposition (SVD). The decomposed signalis separated into source coding streams at step 205 and then mapped ontothe antennae at steps 206-208.

Referring now to FIG. 3, a typical wireless device 300 modifiedaccording to the present invention is illustrated. The device comprisesa transmitter 101 and a receiver 102, both of which are operativelycoupled to a plurality of antennae 303 (only one is shown). The deviceincorporates a feedback circuit 301 that is operatively coupled betweenthe receiver 102 and the transmitter 101 to feedback a received MIMOchannel H using some measurements and feedback from the receiver 102 tothe transmitter 101. A decomposition circuit 302 decomposes an estimatedmatrix H_(n) for the MIMO channel H, and a mapping circuit 303,comprising an SVD circuit 304, that pre-equalizes and separates thedecomposed signal into a plurality of different source coding streamsand then maps the streams onto the plurality of antennae 303 fortransmission by the transmitter 101. The device further comprises amemory 305 for storing matrices pertinent to the decomposition andmapping, e.g., U_(n), V_(n) and D_(n) matrices.

The system and method of the present invention can be used in anywireless multimedia transmission with a MIMO system, such as a wirelesshome network, multimedia streams transmitted over a wireless LAN, and inMIMO systems for wireless multimedia transmission using IEEE 802.11n.Also, in only the CSI-assisted MIMO system, because of thepre-equalization, the decoder needed at the receiver side is muchsimpler than a traditional zero-forced (ZF) or MMSE MIMO decoder. Theonly overhead in the system and method of the present invention is thefeedback of the channel state information from receiver to transmitter.

While the preferred embodiments of the present invention have beenillustrated and described, it will be understood by those skilled in theart that various changes and modifications may be made, and equivalentsmay be substituted for elements thereof without departing from the truescope of the present invention. For example, an absolute time referenceis supplied in an outer layer of a Measurement Request Frame or in aninner layer of an individual basic request of a Measurement RequestElement in any combination with a Measurement Mode. In addition, manymodifications may be made to adapt to a particular situation, such asformat changes of the frames and elements, and the teaching of thepresent invention can be adapted in ways that are equivalent withoutdeparting from its central scope. Therefore it is intended that thepresent invention not be limited to the particular embodiment disclosedas the best mode contemplated for carrying out the present invention,but that the present invention include all embodiments falling withinthe scope of the appended claims.

1. A method for channel state information (CSI) assisted multimediatransmission in a multiple in multiple out MIMO system for wirelessnetwork, comprising the steps of: making a MIMO system channel H (107)from a receiver (102) available at a transmitter (101) (203);decomposing an estimated matrix H_(n) for the MIMO channel H (107)(204); pre-equalizing (106) the decomposed signal; separating thepre-equalized signal into a plurality of different source coding streams(205); and mapping each of the plurality of different source codingstreams onto an antenna for transmission (206).
 2. The method of claim1, wherein said making step further comprises using some measurement andfeedback from the receiver to make the MIMO channel available at thetransmitter.
 3. The method of claim 1, wherein said decomposing stepfurther comprises decomposing the estimated channel matrix H_(n) bymeans of a singular value decomposition (SVD) (204).
 4. The method ofclaim 3, wherein said decomposing step by SVD decomposes H_(n) such thatH_(n)=U_(n)D_(n)V_(n)′, where (a) U_(n) and V_(n) are unitary complexmatrices (i.e. U_(n) U_(n)′=I, etc.) of dimensions R×M and M×Lrespectively, and (b) D_(n) is a real diagonal matrix of dimension M×Mcontaining, in descending order, the non-negative singular values ofH_(n) (which are in fact the square roots of the eigen-values of H_(n)H_(n)′ or H_(n)′ H_(n)), wherein a received signal Y can then beexpressed in terms of a transmitted signal X asY=HX+N=U _(n) D _(n) V _(n) ′X+N where N is the white Gaussian noisewith a zero mean and a variance σ².
 5. The method of claim 4, wherein:said decomposing step by SVD (204) further comprises the steps of— i.performing the SVD by one of the transmitter or the receiver; ii. whenthe performing the SVD step is done by the transmitter the transmittersending the U_(n) matrix to the receiver, iii. when the performing SVDstep is done by the receiver, the receiver performing the steps of— (a)storing the Un and Dn matrices, and (b) feeding back the Vn matrix tothe transmitter.
 6. The method of claim 5, wherein in saidpre-equalizing step further comprises the steps of: since U_(n) andV_(n) are known at the transmitter, multiplying (pre-equalization) withV_(n); and at the receiver side multiplying the received signal withU_(n)′, wherein,U _(n) Y=U _(n) ′H V _(n) X+N=U _(n) ′U _(n) D _(n) V _(n) ′V _(n) X+U_(n) ′V _(n) N=D _(n) X+N.
 7. The method of claim 4, wherein saidseparating step (205) further comprises the step of using the diagonalmatrix D. to separate the signal X into a plurality of different sourcecoding streams.
 8. The method of claim 7, wherein in D_(n) all thesingular values are arranged in descending order and a first stream(signal) thereof in X is allocated a largest gain in the MIMO channel,such that the first steam has a highest SNR for the channel given (207).9. The method of claim 1, wherein said different source coding comprisesat least one source coding selected from the group consisting of finegrained scalability (FGS) (208) and multiple description code (MDC)(207).
 10. The method of claim 9, wherein said plurality of differentsource coding streams comprises a base layer (208) and at least oneenhancement layer.
 11. The method of claim 10, wherein when at least oneof said different source coding is FGS (208), said mapping furthercomprises the substeps of: mapping said base layer onto a stream of saidplurality of different source coding streams having a largestsignal-to-noise ratio (SNR) (208), and mapping said at least oneenhancement layer to others of said plurality of different source codingstreams than the stream having the largest SNR.
 12. Anmultiple-in-multiple-out (MIMO) system for channel state informationCSI-assisted transmission in a wireless network, comprising: a pluralityof antennae (303); a transmitter (101) and a receiver (102) operativelycoupled to said plurality of antennae (303) for respectivelytransmitting and receiving a MIMO channel H; a feedback circuit (301)that feeds back from the receiver the received MIMO channel H to thetransmitter; a decomposition circuit (302) operatively coupled to thefeedback circuit that decomposes an estimated matrix H_(n) of the fedback MIMO channel H; a mapping circuit (303) that pre-equalizes andseparates the decomposed signal into a plurality of different sourcecoding streams and then maps the streams onto the plurality of antennaefor transmission by the transmitter.
 13. The MIMO system of claim 12,wherein the feedback circuit (301) is further configured to use at leastone pre-determined measurement and the received MIMO channel from thereceiver to make the MIMO channel available at the transmitter.
 14. TheMIMO system of claim 12, wherein said decomposition circuit (303) isfurther configured to include a singular value decomposition (SVD)circuit (304) that decomposes the estimated channel matrix H_(n). 15.The MIMO system of claim 14, wherein said SVD decomposes H_(n) (304)such thatH=U_(n)D_(n)V_(n)′ where (a) U_(n) and V_(n) are unitary complexmatrices (i.e. U_(n) U_(n)′=I, etc.) of dimensions R×M and M×Lrespectively, and (b) D_(n) is a real diagonal matrix of dimension M×Mcontaining, in descending order, the non-negative singular values ofH_(n) (which are in fact the square roots of the eigen-values of H_(n)H_(n)′ or H_(n) H_(n)), wherein a received signal Y can then beexpressed in terms of a transmitted signal X asY=HX+N=U _(n) D _(n) V _(n) ′X+N where N is the white Gaussian noisewith a zero mean and a variance a σ².
 16. The MIMO system of claim 15,wherein: said system further comprises a memory (305); and saiddecomposition circuit (304) is further configured to— i. be invoked byat least one of the transmitter (101) and the receive (102); ii. storein the memory (305) the Un, Vn and Dn matrices each by at least one ofthe transmitter (101) and the receiver (102) for future use by at leastone of the transmitter (101) and the receiver (102).
 17. The MIMO systemof claim 16, wherein in said mapping circuit (303) is further configuredto: pre-equalize by multiplying with V_(n), since U_(n) and V_(n) areknown at the transmitter; and multiply the received signal with U_(n)′at the receiver side wherein,U _(n) ′Y=U _(n) ′H V X+N=U _(n) ′U _(n) D _(n) V _(n) ′V _(n) X+U _(n)′V _(n) N=D _(n) X+N.
 18. The MIMO system of claim 16, wherein saidmapping circuit (303) is further configured to use the diagonal matrixDn to separate the signal X into a plurality of different source codingstreams (206).
 19. The MIMO system of claim 18, wherein in D_(n) all thesingular values are arranged in descending order and a first stream(signal) thereof in X is allocated a largest gain in the MIMO channelsuch that the first steam has a highest SNR for the channel given (206).20. The MIMO system of claim 12, wherein said different source codingcomprises at least one source coding selected from the group consistingof fine grained scalability (FGS) (208) and multiple description code(MDC) (207).
 21. The MIMO system of claim 20, wherein said plurality ofdifferent source coding streams comprises a base layer and at least oneenhancement layer.
 22. The MIMO system of claim 21, wherein when atleast one of said different source coding is FGS, said mapping circuitis further configured to: map said base layer onto a stream of saidplurality of different source coding streams having a largestsignal-to-noise ratio (SNR) (208), and map said at least one enhancementlayer to others of said plurality of different source coding streamsthan the stream having the largest SNR.
 23. An device for channel stateinformation (CSI) assisted transmission in a wireless network,comprising: a decomposition circuit (302) to estimate a channel matrixH_(n) of a MIMO channel signal H received by a receiver (102) andprovide a decomposed signal therefrom; a mapping circuit (303) thatpre-equalizes and separates the decomposed signal into a plurality ofdifferent source coding streams and then uses CSI to map the streamsonto a plurality of antennae for transmission by a transmitter (101).24. The device of claim 23, wherein said decomposition circuit (302) isfurther configured to include a singular value decomposition (SVD)circuit that decomposes the estimated channel matrix H_(n) such thatU_(n)=U_(n)D_(n)V_(n)′ where (a) U_(n) and V_(n) are unitary complexmatrices (i.e. U_(n) U_(n)′=I, etc.) of dimensions R×M and M×Lrespectively, and (b) D_(n) is a real diagonal matrix of dimension M−Mcontaining, in descending order, the non-negative singular values ofH_(n) (which are in fact the square roots of the eigen-values of H_(n)H_(n)′ or H_(n)′ H_(n)), wherein a received signal Y can then beexpressed in terms of a transmitted signal X asY=HX+N=U _(n) D _(n) V _(n) ′X+N where N is the white Gaussian noisewith a zero mean and a variance a σ².
 25. The device of claim 24,wherein: said device further comprises a memory (304); and saiddecomposition circuit (302) is further configured to— i. be invoked byat least one of the transmitter (101) and the receiver (102); ii. storein the memory (304) the Un, Vn and Dn matrices each by at least one ofthe transmitter and the receiver for future use by at least one of thetransmitter (101) and the receiver (102).
 26. The device of claim 25,wherein in said mapping circuit (303) is further configured to:pre-equalize by multiplying with V_(n), since U_(n) and V_(n) are knownat the transmitter; and multiply the received signal with U_(n)′ at thereceiver side, wherein,U _(n) ′Y=U _(n) ′H V _(n) X+N=U _(n) ′U _(n) D _(n) V _(n) ′V _(n) X+U_(n) ′V _(n) N=D _(n) X+N.